Why not install a matched pair of 4 GB modules? Not sure why OWC doesn't list that possibility.
I am leaning toward the matched pair (OWC does have them) but apparently I can also go to 6GB, which is tempting IF there's a real advantage. However, if it's marginal and has the potential for other headaches.........
ryck
"What Were Once Vices Are Now Habits" The Doobie Brothers